Static inverter wherein a plurality of square waves are so summed as to produce a sinusoidal output wave

Abstract

This invention relates generally to power inverting devices and more particularly, to static inverting devices which produce an output wave shape which closely approximates a sine wave.

What is claimed and is desired to be covered by United States Letters Patent is as follows: 
     
       1. In an apparatus for inverting unidirectional potential into alternating potential of a predetermined frequency, an N number of phase displaced voltage generators, N being at least 3, each said generator having a square shaped output voltage wave of said predetermined frequency .Iadd.and same amplitude.Iaddend., and means .Iadd.for dimensioning said square shaped output voltages in amplitude, and for .Iaddend.combining the outputs of said generators to produce a resulting voltage wave of stepped configuration, the magnitudes of .Iadd.dimensioned .Iaddend.said output voltage waves being so related to the magnitudes of the phase displacement of said generators that said resulting wave generally follows the configuration of a sine wave and contains a lesser quantity of harmonics than are contained in said output waves of said generators. 
     
     
       2. The combination of claim 1 in which there is provided means actuating said generators in succession at intervals of 180°/N. 
     
     
       3. The combination of claim 1 in which there is provided means actuating said generators in succession at intervals of 180°/(N+1). 
     
     
       4. In an apparatus for inverting unidirectional potential into alternating potential; a pair of output connections; at least 3 inverting networks; each said network comprising a pair of input terminals adapted to be energized from a source of unidirectional potential, a pair of output terminals, and first and second current conducting paths connecting said input terminals to said output terminals; each said path including a current controlling device having a closed circuit condition in which said path is effective to conduct and an open circuit condition in which said path is ineffective to conduct substantial current; each of said first paths being effective when its said device is conducting to energize its said output terminals in a first polarity; each of said second paths being effective when its said device is conducting to energize its said output terminals in a second polarity; means sequentially rendering all of said first paths conducting in a predetermined timed sequence and thereafter all of said second paths conducting in said predetermined timed sequence in a chain-like manner; and means connecting at least certain of said pairs of output terminals in additive series arrangement between said output connections, said certain terminals being those of certain of said inverting networks selected from those of said networks having a total phase displacement which is not in excess of 180°. 
     
     
       5. In an apparatus for inverting unidirectional potential into alternating potential, and N number of square wave voltage sources, means interlocking said sources whereby the said sources are actuated in sequence to provide a series of voltages of a first polarity and thereafter of a second polarity, said interlocking means being so arranged that the time intervals between the voltage changes of any two adjacent successive-to-be-actuated ones of said sources is equal to π/N radians, a P number of series connected groups of said sources, each said group being arranged to be energized by the combined voltages of the said sources which comprise the respective said group, each said group comprising voltages from all of and solely those of said sources which change in potential from said first to said second polarity within a time interval not greater than π/2 radians from the point at which said respective group voltage changes polarity and which voltages have an appreciable magnitude, the angular displacement between the instant at which any two adjacent successive groups of said voltage waves change from said first to a second polarity being 2π/P radians, the magnitudes of the output voltages of said source of any said group being represented by the arithmetic product of (1-cos π/N) and the cosine of the electrical angle between the point at which the respective said group voltage changes polarity from said first to said second polarity and the point at which the particular source within said respective group changes from said first to said second polarity. 
     
     
       6. In an apparatus for inverting unidirectional potential into alternating potential, an N number of square wave voltage sources, the voltage of each said source having a phase angle with respect to an arbitrary reference and a predetermined magnitude, means interlocking said sources whereby the said sources are actuated in sequence to provide a series of voltages of a first polarity and thereafter of a second polarity, said interlocking means being so arranged that the time intervals between the voltage changes of any two of said sources is equal to π/N radians, a P number of series connected groups of said output terminals to provide a P number of group output voltages each having a phase angle with respect to said reference, each said group being arranged to be energized by the combined voltages of said sources which comprise the respective said group, each said group comprising the said sources which have their phase angles electrically spaced less than π/2 radians from said phase angle of the respective said group of which it is a part the difference in phase angle between phase angles of any two adjacent successive said groups being 2π/P radians, the magnitudes of said voltages of said sources of any said group being represented by the arithmetic product of (1-cos π/N) and the cosine of the difference in said phase angle between that of the particular group and that of said particular source of said particular group, said phase angle of each said group being located π/2 radians away from said phase angle of the said sources included in the respective said group. 
     
     
       7. In an apparatus for inverting unidirectional potential into alternating potential; a pair of output connections; an N number of inverting networks; each said network comprising a pair of input terminals adapted to be energized from a source of unidirectional potential, a pair of output terminals, and first and second current conducting paths connecting said input terminals to said output terminals; each said path including a current controlling device having a closed circuit condition in which said path is effective to conduct and an open circuit condition in which said path is ineffective to conduct substantial current; means sequentially rendering said first paths conducting and thereafter said second paths conducting in timed sequence; said timed sequence at which said second paths are rendered; and means connecting said pairs of output terminals in series between said output connections; the potentials between said pairs of output terminals being so related that all of the harmonics in the voltage appearing between said output connections below a value 2N-1 are neutralized. 
     
     
       8. In an apparatus for inverting unidirectional potential into alternating potential; a pair of output connections; an N number of inverting networks; each said network comprising a pair of input terminals adapted to be energized from a source of unidirectional potential, a pair of output terminals, and first and second current conducting paths connecting said input terminals to said output terminals; each said path including a current controlling device having a closed circuit condition in which said path is effective to conduct and an open circuit condition in which said path is ineffective to conduct substantial current; means sequentially rendering said current controlling devices of said first paths in closed circuit condition and said current controlling devices of said second paths in open circuit conditions in timed sequence; said sequentially rendering means thereafter rendering said current controlling devices of said second paths in closed circuit conditions and said current controlling devices of said first paths in open circuit condition in timed sequence; said sequentially rendering means providing a greater time interval between the rendering conductive of the last to be rendered conductive of said first paths and the rendering conductive of the first to be rendered conductive of said second paths than the time interval of said timed sequence at which said first paths are rendered conductive, said sequentially rendering means also providing a greater time interval between the rendering conductive of the last to be rendered conductive of said second paths and the rendering conductive of the first to be rendered conductive of said first paths than the time interval of said timed sequence at which said second paths are rendered conductive, and means connecting said pairs of output terminals in series between said output connections, the potential between one of said pair of output terminals being 90° out of phase with respect to the phase of the potential between said output connections, the potentials between said pairs of output terminals of said inverters being proportioned to provide an output wave shape in which all of the harmonics below a value 2N-1 are neutralized. 
     
     
       9. In an apparatus for inverting unidirectional potential into alternating potential; a pair of output connections; a plurality of inverter networks; each of said network comprising a pair of input terminals adapted to be energized from a source of unidirectional potential, a transformer having primary winding means and secondary winding means, and first and second current conducting paths connecting said input terminals to said primary winding means; each said path including current controlling means having a closed circuit condition in which said path is effective to conduct and an open circuit condition in which said path is ineffective to conduct substantial current; each said controlling means having a control circuit operable upon a change in the energization thereof to place the associated said controlling means in its said closed circuit condition; means generating a series of equally spaced impulses, interconnecting means including time delay means connecting said generating means to said controlling means for changing the energization of said controlling means whereby said controlling means are placed in their said closed circuit conditions; said interconnecting means further including gating means whereby solely one of said controlling means is rendered effective for each said impulse; said gating means being effective to render said generating means effective to actuate sequentially into their said closed conditions said controlling means associated with said first paths and to thereafter actuate sequentially into their said closed conditions said controlling means associated with said second paths; each said inverter network including an impedance controlling means connected to one of said winding means whereby the impedance of said secondary winding means to current flow may be reduced; means connecting said secondary winding means in series circuit to said output connections; and means actuated in timed sequence with the magnitude of the delay afforded by said time delay means for actuating said impedance controlling means to reduce the impedance of said secondary winding means for an interval equivalent to the magnitude of said delay afforded by said time delay means. 
     
     
       10. In an apparatus for inverting unidirectional potential into alternating potential; a pair of output connections; a plurality of inverter networks; each said network comprising a pair of input terminals adapted to be energized from a source of unidirectional potential, a transformer having primary winding means and secondary winding means, and first and second current conducting paths connecting said input terminals to said primary winding means; each said path including current controlling means having a closed circuit condition in which said path is effective to conduct and an open circuit condition in which said path is ineffective to conduct substantial current; each said controlling means having a control circuit operable upon a change in the energization thereof to place the associated said controlling means in its said closed circuit condition; means generating a series of equally spaced impulses, interconnecting means including time delay means connecting said generating means to said controlling means for changing the energization of said controlling means whereby said controlling means are placed in their said closed circuit conditions; said interconnecting means further including gating means whereby solely one of said controlling means is rendered effective for each said impulse; said gating means being effective to render said generating means effective to actuate sequentially into their said closed conditions said controlling means associated with said first paths and to thereafter actuate sequentially into their said closed conditions said controlling means associated with said second paths; said gating means acting to provide a double length time interval between the actuation of said controlling means associated with said first paths and the actuation of said controlling means associated with said second paths; said gating means acting to actuate said controlling means of said second paths in the same sequence as said controlling means of said first paths; each said inverter network including an impedance controlling means connected to one of said winding means whereby the impedance of said secondary winding means to current flow may be reduced; means connecting said secondary winding means in series circuit to said output connections; and means actuated in timed sequence with the magnitude of the delay afforded by said time delay means for actuating said impedance controlling means to reduce the impedance of said secondary winding means for an interval equivalent to the magnitude of said delay afforded by said time delay means. 
     
     
       11. In an apparatus for inverting unidirectional potential into polyphase alternating potential; a plurality of output conductors; a plurality of flip-flop devices; each said flip-flop device having power output terminals, power input terminals, control input terminals, and a pair of current paths interconnecting said power input terminals with said power output terminals; each said path including a current controlling device having a control circuit and a power circuit controlling current flow through the said path with which said current device is associated; each said flip-flop device including means connecting said control circuits of its said current controlling devices to its said control input terminals; and output transformer individual to each said flip-flop device; each said transformer including input and output winding means; a plurality of network means individually connecting said transformers to said flip-flop devices; control means connected to said control input terminals and operable to actuate a first, a second, a third, a fourth, a fifth, and a sixth of said flip-flops in sequence from a first operating condition in which first paths are nonconducting and said second paths are conducting into a second operating condition in which said second paths are nonconducting and said first paths are conducting; said control means thereafter being operable to actuate said first, said second, said third, said fourth, said fifth and said sixth flip-flop in sequence from their said second operating conditions to their said first operating conditions; each said network means being arranged to energize its said transformer at a first polarity as a consequence of its said flip-flop being actuated to its said first operating condition and at a second polarity as a consequence of its said flip-flop being actuated to its said second operating condition; means connecting a first portion of said output winding means of said first, said second, said third, said fourth, and said fifth transformer in between a first pair of said plurality of conductors; means connecting a second portion of said output winding means of said fifth, said sixth, said first, said second, and said third transformers between a second pair of said plurality of conductors; and means connecting a third portion of said output winding means of said third, said fourth, said fifth, said sixth, and said first transformer between a third pair of said plurality of conductors. 
     
     
       12. In an apparatus for inverting unidirectional potential into polyphase alternating potential; a plurality of output conductors; a plurality of flip-flop devices; each said flip-flop device having power output terminals, power input terminals, control input terminals, and a pair of current paths interconnecting said power input terminals with said power output terminals; each said path including a current controlling device having a control circuit and a power circuit controlling current flow through the said path with which said current device is associated; each said flip-flop device including means connecting said control circuits of its said current controlling devices to its said control input terminals; and output transformer individual to each said flip-flop device; each said transformer including input and output winding means; a plurality of network means individually connecting said transformers to said flip-flop devices; control means connected to said control input terminals and operable to actuate a first, a second, a third, a fourth, a fifth, and a sixth of said flip-flops in sequence from a first operating condition in which first paths are nonconducting and said second paths are conducting into a second operating condition in which said second paths are nonconducting and said first paths are conducting; said control means thereafter being operable to actuate said first, said second, said third, said fourth, said fifth and said sixth flip-flop in sequence from their said second operating conditions to either said first operating conditions; each said network means being arranged to energize its said transformer at a first polarity as a consequence of its said flip-flop being actuated to its said first operating condition and at a second polarity as a consequence of its said flip-flop being actuated to its said second operating condition; means connecting a first portion of said output winding means of said first, said second, said third, said fourth, and said fifth transformer in between a first pair of said plurality of conductors; means connecting a second portion of said output winding means of said fifth, said sixth, said first, said second, and said third transformers between a second pair of said plurality of conductors; means connecting a third portion of said output winding means of said third, said fourth, said fifth, said sixth, and said first transformer between a third pair of said plurality of conductors, voltage reducing means operatively associated with said power output input terminals for controlling the magnitude of the potential supplied to said flip-flop; and means responsive to an operating condition of said output conductors for controlling said regulating means. 
     
     
       13. In an apparatus for inverting unidirectional potential into polyphase alternating potential; a plurality of output conductors; a plurality of flip-flop devices; each said flip-flop device having power output terminals, power input terminals, control input terminals, and a pair of current paths interconnecting said power input terminals with said power output terminals; each said path including a current controlling device having a control circuit and a power circuit controlling current flow through the said path with which said current device is associated; each said flip-flop device including means connecting said control circuits of its said current controlling devices to its said control input terminals; and output transformer individual to each said flip-flop device; each said transformer including input and output winding means; a plurality of network means individually connecting said transformers to said flip-flop devices; control means connected to said control input terminals and operable to actuate a first, a second, a third, a fourth, a fifth, and a sixth of said flip-flops in sequence from a first operating condition in which paths are nonconducting and said second paths are conducting into a second operating condition in which said second paths are nonconducting and said first paths are conducting; said control means thereafter being operable to actuate said first, said second, said third, said fourth, said fifth and said sixth flip-flop in sequence from their said second operating conditions to their said first operating conditions; each said network means being arranged to energize its said transformer at a first polarity as a consequence of its said flip-flop being actuated to its said first operating condition and at a second polarity as a consequence of its said flip-flop being actuated to its said second operating condition; means connecting a first portion of said input winding means of said first, said second, said third, said fourth, and said fifth transformer in between a first pair of said plurality of conductors; means connecting a second portion of said output winding means of said fifth, said sixth, said first, said second, and said third transformers between a second pair of said plurality of conductors; means connecting a first portion of said output winding means of said third, fourth, said fifth, said sixth, and said first transformer between a third pair of said plurality of conductors, voltage regulating means operatively associated with said power input terminals; said regulating means having a first operating conditions in which potential of a first magnitude is supplied to said flip-flop and a second condition in which potential of a second magnitude is supplied to said flip-flops; and means responsive to current flow in at least one of said output conductors for determining the one of said operating conditions of said voltage regulating means which is effective. 
     
     
       14. In a network for inverting unidirectional potential to alternating polarity; a flip-flop network; a driver network; an output transformer having input winding means and output winding means; said flip-flop network comprising a pair of power input terminals, adapted to be connected to a source of unidirectional potential, first and second groups of power output terminals, a control input terminal, a pair of current controlling devices each having a main current path and a pair of control terminals, a first current conducting path connecting said input terminals to each of said groups of output terminals, and including said current path of a first of said pair of current controlling devices, a second current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a second of said pair of current controlling devices, said second path being operative to energize said output terminals at a polarity different from the energization thereof by said first path; means operatively connected to said terminals of said current controlling devices and effective to periodically reverse the relative conductive conditions of said main current paths, said driver network comprising a pair of power input terminals, a group of power output terminals, a pair of current controlling devices having power paths and control terminals, a first power path connecting said driver input terminals to said driver output terminals and including said power paths of a first of said pair of driver current controlling devices, a second power path connecting said driver input terminals to said driver output terminals and including said power path of a second of said pair of driver current controlling devices, said second path of said driver being effective to energize said output terminals of said driver at a polarity opposite to the energization of said first path of said driver; means including time delay means interconnecting said control terminals of said driver to said first group of output terminals of said flip-flop network and effective at one polarity of energization of said first group of flip-flop output terminals to render said power path of said first current controlling device of said driver conductive and effective at the opposite polarity of energization of said first group of flip-flop output terminals to render said power path of said second current controlling device of said driver conductive; means connecting said input winding means of said transformer to said output terminals of said driver for energization of said transformer at alternating polarities as a consequence of the alternating polarity of energization of said driver output terminals; a switching network connected across at least a portion of one of said winding means of said transformer and having current conducting and a current interrupting operating conditions; and means actuated by said time delay means connecting said second group of output terminals to said switching network and effective to maintain said switching network in its said current conducting condition during the timing out period of said time delay means and thereafter to maintain said switching network in its said current interrupting condition. 
     
     
       15. In a network for inverting unidirectional potential to alternating polarity; a flip-flop network; a driver network; an output transformer having input winding means and output winding means; said flip-flop network comprising a pair of power input terminals, adapted to be connected to a source of unidirectional potential, first and second groups of power output terminals, a control input terminal, a pair of current controlling devices each having a main current path and a pair of control terminals, a first current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a first of said pair of current controlling devices, a second current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a second of said pair of current controlling devices, said second path being operative to energize said output terminals at a polarity different from the energization thereof by said first path; means operatively connected to said terminals of said current controlling devices and effective to periodically reverse the relative conductive conditions of said main current paths; and driver network comprising a pair of power input terminals, a group of power output terminals, a pair of current controlling devices having power paths and control terminals, a first power path connecting said driver input terminals to said driver output terminals and including said power paths of a first of said pair of driver current controlling devices, a second power path connecting said driver input terminals to said driver output terminals and including said power path of a second of said pair of driver current controlling devices, said second path of said driver being effective to energize said output terminals of said driver at a polarity opposite to the energization of said first path of said driver; means including time delay means interconnecting said control terminals of said driver to said first group of output terminals of said flip-flop network and effective at one polarity of energization of said first group of flip-flop output terminals to render said power path of said first current controlling device of said driver conductive and effective at the opposite polarity of energization of said first group of flip-flop output terminals to render said power path of said second current controlling device of said driver conductive; means connecting said input winding means of said transformer to said output terminals of said driver for energization of said transformer at alternating polarities as a consequence of the alternating polarity of energization of said driver output terminals; a switching network connected across at least a portion of one of said winding means of said transformer and having current conducting and a current interrupting operating conditions; means actuated by said time delay means connecting said second group of output terminals to said switching network and effective to maintain said switching network in its said current conducting condition during the timing out period of said time delay means and thereafter to maintain said switching network in its said current interrupting condition; and means responsive to an operating characteristic of said output winding of said transformer for regulating the voltage applied to said input terminals of said flip-flop. 
     
     
       16. In a network for inverting unidirectional potential to alternating polarity; a flip-flop network; a driver network; an output transformer having input winding means and output winding means; said flip-flop network comprising a pair of power input terminals, adapted to be connected to a source of unidirectional potential, first and second groups of power output terminals, a control input terminal, a pair of current controlling devices each having a main current path and a pair of control terminals, a first current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a first of said pair of current controlling devices, a second current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a second of said pair of current controlling devices, said second path being operative to energize said output terminals at a polarity different from the energization thereof by said first path; means operatively connected to said terminals of said current controlling devices and effective to periodically reverse the relative conductive conditions of said main current paths; said driver network comprising a pair of power input terminals, a group of power output terminals, a pair of current controlling devices having power paths and control terminals, a first power path controlling said driver input terminals to said driver output terminals and including said power paths of a first of said pair of driver current controlling devices, a second power path connecting said driver input terminals to said driver output terminals and including said power path of a second of said pair of driver current controlling devices, said second path of said driver being effective to energize said output terminals of said driver at a polarity opposite to the energization of said first path of said driver; means including time delay means interconnecting said control terminals of said driver to said first group of output terminals of said flip-flop network and effective at one polarity of energization of said first group of flip-flop output terminals to render said power path of said first current controlling device of said driver conductive and effective at the opposite polarity of energization of said first group of flip-flop output terminals to render said power path of said second current controlling device of said driver conductive; said time delay means being adjustable to adjust the length of its timing out periods; means connecting said input winding means of said transformer to said output terminals of said driver for energization of said transformer at alternating polarities as a consequence of the alternating polarity of energization of said driver output terminals; a switching network connected across at least a portion of one of said winding means of said transformer and having current conducting and a current interrupting operating conditions, means actuated by said time delay means connecting said second group of output terminals to said switching network and effective to maintain said switching network in its said current conducting condition during the timing out period of said time delay means and thereafter to maintain said switching network in its said current interrupting condition; and means responsive to an increase in the magnitude of current flowing in one of said transformer winding means above a first predetermined maximum current magnitude for increasing said timing out period of said time delay means. 
     
     
       17. In a network for inverting unidirectional potential to alternating polarity; a flip-flop network; a driver network; an output transformer having input winding means and output winding means; said flip-flop network comprising a pair of power input terminals, adapted to be connected to a source of unidirectional potential, first and second groups of power output terminals, a control input terminal, a pair of current controlling devices each having a main current path and a pair of control terminals, a first current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a first of said pair of current controlling devices, a second current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a second of said pair of current controlling devices, said second path being operative to energize said output terminals at a polarity different from the energization thereof by said first path; means operatively connected to said terminals of said current controlling devices and effective to periodically reverse the relative conductive conditions of said main current paths; said driver network comprising a pair of power input terminals, a group of power output terminals, a pair of current controlling devices having power paths and control terminals, a first power path connecting said driver input terminals to said driver output terminals and including said power paths of a first of said pair of driver current controlling devices, a second power path connecting said driver input terminals to said driver output terminals and including said path of a second of said path of driver current controlling devices, said second path of said driver being effective to energize said output terminals of said driver at a polarity opposite to the energization of said first path of said driver; means including time delay means interconnecting said control terminals of said driver to said first group of output terminals of said flip-flop network and effective at one polarity of energization of said first group of flip-flop output terminals to render said power path of said first current controlling device of said driver conductive and effective at the opposite polarity of energization of said group of flip-flop output terminals to render said power path of said second current controlling device of said driver conductive; said time delay means being adjustable to adjust the length of its timing out periods; means connecting said input winding means of said transformer to said output terminals of said driver for energization of said transformer at alternating polarities as a consequence of the alternating polarity of energization of said driver output terminals; a switching network connected across at least a portion of one of said winding means of said transformer and having current conducting and a current interrupting operating conditions; means actuated by said time delay means connecting said second group of output terminals to said switching network and effective to maintain said switching network in its said current conducting condition during the timing out period of said time delay means and thereafter to maintain said switching network in its said current interrupting condition; and means responsive to an increase in the magnitude of current flowing in one of said transformer winding means above a first predetermined maximum current magnitude for increasing said timing out period of said time delay means; and means responsive to an increase in the magnitude of current flowing in one of said transformer winding means above a second predetermined maximum current magnitude less than said first predetermined magnitude for increasing the voltage supplied to said power input terminals of said flip-flop. 
     
     
       18. In a network for inverting unidirectional potential to alternating polarity; a flip-flop network; a driver network; an output transformer having input winding means and output winding means; said flip-flop network comprising a pair of power input terminals, adapted to be connected to a source of unidirectional potential, first and second groups of power output terminals, a control input terminal, a pair of current controllling devices each having a main current path and a pair of control terminals, a first current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a first of said pair of current controlling devices, a second current conducting path connecting said input terminals to each of said groups of output terminals and including said current path of a second of said pair of current controlling devices, said second path being operative to energize said output terminals at a polarity different from the energization thereof by said first path; means operatively connected to said terminals of said current controlling devices and effective to periodically reverse the relative conductive conditions of said main current paths; said driver network comprising a pair of power input terminals, a group of power output terminals, a pair of current controlling devices having power paths and control terminals, a first power path connecting said driver input terminals to said driver output terminals and including said power paths of a first of said pair of driver current controlling devices, a second power path connecting said driver input terminals to said driver output terminals and including said power path of a second of said path of driver current controlling devices, said second path of said driver being effective to energize said output terminals of said driver at a polarity opposite to the energization of said first path of said driver; first and second saturating core inductive devices; each said saturating devices having a plurality of control windings inductively coupled together through said core; means including one of said control windings of said first saturating device interconnecting said control terminals of said driver to said first group of output terminals of a first of said current controlling devices of said flip-flop network and effective at one polarity of energization of said first group of flip-flop output terminals to render said power path of said first current controlling device of said driver conductive means including one of said control windings of said second saturating device interconnecting said control terminals of a second of said current controlling device of said driver to said first group of output terminals of said flip-flop network and effective at the opposite polarity of energization of said first group of flip-flop output terminals to render said power path of said second current controlling device of said driver conductive; means connecting said input winding means of said transformer to said output terminals of said driver for energization of said transformer at alternating polarities as a consequence of the alternating polarity of energization of said driver output terminals; a switching network connected across at least a position of one of said winding means of said transformer and having current conducting and a current interrupting operating conditions; means actuated by a second of said control windings of each of said saturating devices and effective to maintain said switching network in its said current conducting condition prior to saturation of said devices and thereafter to maintain said switching network in its said current interrupting condition; means connected to a third control winding of each of said devices and responsive to an increase in the magnitude current flowing in one of said transformer winding means above a first predetermined maximum current magnitude to alter the energization of said third control windings to increase the current flow through said first control windings necessary to saturate said cores; and means responsive to the magnitude of current flowing in one of said transformer winding means above a second predetermined maximum current magnitude to increase the potential supplied to said power input terminals of said flip-flop network; said second magnitude being less than said first magnitude. 
     
     
       19. In an apparatus for inverting unidirectional potential into alternating potential, N number of square wave voltage sources each having an output voltage of predetermined magnitude, means phasing said sources such that the phase angle between the vectors of any two adjacent successive voltages of said output voltages starting with a first thereof and ending with the Nth thereof are equal to other, said angles being of a magnitude between π/N and π/N+1 radians, a pair of output terminals, and means connecting said output voltages of all of said sources in additive series circuit between said terminals to provide a stepped voltage wave approximating a sine wave, said predetermined magnitude of each of said N sources satisfying the equation .[.M x  =(1-cos φ).]. .Iadd.M x  =(1-cos π/N) cos θ x  .Iaddend. where M x  equals the relative magnitude of the square wave of any source x having an acute phase angle θ x  with respect to a voltage vector which is located centrally of and at an acute angle to all of said voltage vectors of said sources and where φ equals said angle between said adjacent successive sources. 
     
     
       20. In an apparatus for inverting unidirectional potential into alternating potential, N number of square wave voltage sources each having an output voltage of predetermined magnitude, means phasing said sources such that the phase angle between the vectors of any two adjacent successive voltages of said output voltages starting with a first thereof and ending with the Nth thereof are equal to each other, a pair of output terminals, and means connecting in series additive relation the output voltages of all of and solely those of said voltage sources which lie within an angle between plus and minus 90° of the phase angle of the vector of the voltage which exists between said output terminals and which have a substantial magnitude, said predetermined magnitude of each said source satisfying the equation .[.M x  =(1 cos π/N) cos (θ x ).]. .Iadd.M x  =(1-cos π/N) cos θ x  .Iaddend. where M x  equals the relative magnitude of the square wave of source x having an acute phase angle θ x  with respect to the phase of said sine wave at said output terminals. 
     
     
       21. In an apparatus for inverting unidirectional potential into polyphase alternating potential of P phases; P pairs of output connections for said alternating potential; an N number of inverter networks; each said network comprising a pair of input terminals adapted to be energized from a source of unidirectional potential, a transformer having primary winding means and secondary winding means, and first and second current conducting paths connecting said input terminals to said primary winding means; each said path including current controlling means having a closed circuit condition in which said path is effective to energize said primary winding means to induce a voltage in its associated said secondary winding means and an open circuit condition in which said path is .[.effective.]. .Iadd.ineffective .Iaddend.to conduct substantial current; the instantaneous polarity of the voltage induced in said secondary winding means being dependent upon the relative conductive conditions of the said first and second paths with which said transformer is associated; means associated with said current controlling means and effective to render sequentially into closed circuit conditions said current controlling means associated with said first paths and thereafter to render sequentially into closed circuit condition said current controlling means associated with said second paths; the interval between the rendering of any two successive current controlling means into their closed circuit conditions being equal; circuit means individually connecting together in series additive relation portions of said secondary winding means to provide groups; said groups being individually connected between said P pairs of output connections; each said group including portions of said secondary winding means of at least N-1 of said transformers; the magnitudes of the output voltages derived from said secondary winding means portions satisfying the equation M x  =(1-cos π/N) cos θ x  where M x  equals the amplitude of the voltage of a secondary winding portion x having an acute phase angle θ x  with respect to the phase angle of the voltage to be established between the said pairs of output connections with which said secondary winding portion x is associated. 
     
     
       22. The combination of claim 21 in which N/P is an integer and in which the phase angle between any two successive adjacent voltages at said output connections is equal to 2π/P and in which the phase of the output voltage of at least one of said secondary winding portions which is associated with each said group has an angle of π/2 radians with respect to the output voltage of the said group with which it is a part. 
     
     
       23. Means for converting the output of a DC power source to a quasi sinusoidal stepped wave power output, said wave having two n steps in each cycle, n being an odd number, the riser of each step having a chosen amplitude comprising means in circuit with said source for generating n square wave voltages having like frequencies and being 180/n degrees displaced in phase with respect to each other, n power inverters, means for applying the output of said DC source and a respective one of said square wave voltages to each of said power inverters, one of said inverters responsive to its applied DC source output and applied respective square wave voltages for deriving an output having the amplitude of the initial step of a cycle of said stepped wave, respective pairs of the other power inverters responsive to their respective DC source outputs and their applied respective square wave voltages for deriving first and second outputs which are equal to each other and equal to one half the amplitude of the riser of a chosen step in said stepped wave, and means for vectorially combining said derived outputs in a phase relationship such that the initial portion of one half cycle and having the width of a step of the initial step power inverter output is combined with said first outputs in one polarity and with said second outputs in the opposite polarity, said second outputs having respectively half the amplitudes of the risers of succeeding steps are timed to change polarity at their corresponding steps, said initial step outputs are timed to change polarity at the first step of the next half cycle, and said first outputs are timed to change polarity at their corresponding steps respectively immediately preceding the change of polarity of said initial step output. 
     
     
       24. An arrangement for inverting a unidirectional wave into an alternating wave of a predetermined frequency comprising at least 3 wave generators, each of said generators producing a square shaped output .Iadd.voltage .Iaddend.wave of said predetermined frequency .Iadd.and of same amplitude.Iaddend., means .Iadd.for serially .Iaddend.combining the output waves of said generators to produce a resulting wave of stepped configuration, means for differently dimensioning the time occurrence of each of said square waves so that the discontinuties in the form of said resulting wave occur at selected integral multiples of a given electrical angle, and means .Iadd.responsive to each of said square shaped output voltages .Iaddend.for dimensioning the change in amplitude of said resulting wave at times corresponding to the occurrence of each discontinuity to be proportional to the cosine of the electrical angle corresponding to the time of occurrence of each such discontinuity. 
     
     
       25. An arrangement for inverting unidirectional potential into three phase alternating potential of a predetermined frequency comprising first.[.,.]. means for producing a first resulting voltage wave of stepped configuration, said first means comprising a first plurality of voltage generators, each of said generators producing a square shaped output voltage wave of said predetermined frequency .Iadd.and of same amplitude.Iaddend., means combining the output waves of said generators to produce said first resulting voltage wave of stepped configuration, means for differently dimensioning the time occurrence of each of said square waves so that the discontinuities in said first resulting wave occur at selected integral multiples of a given electrical angle, and means .Iadd.responsive to each of said square shaped output voltage waves .Iaddend.for dimensioning the change in amplitude of said resulting wave at times corresponding to the occurrence of each discontinuity to be proportional to the cosine of the electrical angle corresponding to the time of occurrence of each such discontinuity, second means and third means for producing respectively second and third resulting voltage waves of stepped configuration identical to said first resulting voltage wave, and means for providing a phase displacement of 120 electrical degrees between said first, second and third resulting waves. .Iadd.26. The apparatus of claim 1 with means for controlling each of said generators for modifying the overall amplitude of said alternating potential in relation to said unidirectional potential. .Iaddend..Iadd.27. The apparatus of claim 24 with means for equally varying the duration of said square shaped voltage output waves for modifying the overall amplitude of said alternating wave in relation to said unidirectional wave. .Iaddend..Iadd.28. The apparatus of claim 25 with means for controlling each of said generators to equally modify the width of said square shaped output voltage waves for altering the overall amplitude of said three phase alternating potential in relation to said unidirectional potential. .Iaddend.